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External input circulator recommendation

mikemac52mikemac52 Member Posts: 37
Looking for a circulator that has 0-10 volt or pwm input control that Doesn't cost 600+ dollars. Looking to have a go at hot water recirculation. Do they exist?



  • Dave H_2Dave H_2 Member Posts: 388
    I have a couple of questions,

    What size circ is needed?
    Why would you need 0-10 for a DHW recirc? Where is the data coming from to either speed up or slow down the circ.

    Dave H.
    Dave H
  • mikemac52mikemac52 Member Posts: 37
    First, I'm going to make this way more complicated than necessary...
    just cause I can. :smile: Well, and hopefully save water and fuel.

    I may eventually run this through a PLC because I want 2 temp sensor points and would prefer to use pwm. But to start, 3 relays(perhaps 4), a temp sensor, flow detector and timer.

    During two prime time periods, the pump will receive a low voltage to pump the minimum gpm to offset pipe losses and be controlled by temp only. My indirect water heater had a readout issue (12 degrees high) and they sent a new controller with rtd. Use the old one and set it to cut out at 122F (110F real temp).

    During the rest of the time, a flow sensor will be put in series with the temp relay and when they both call, A higher voltage will be sent to the pump for full gpm to reduce the time the hot water takes to get to the sink. Semi on demand.

    My house is 100 years old and and the recirculation pipe is not ideal. It just runs to the furthest part of the plumbing in the basement. The way the crazy pipes run though, It is approx. 35-40 pipe feet and we can wait 2 minutes for hot water at the kitchen sink when its been idle. Water is expensive here in the city. The furthest riser going up to the 3rd floor is only 1/2 inch. So the 3/4 recirc. pipe will help cut that time down, hopefully quite a bit.

    Plc will be much neater as for now I will just be using voltage dividers which should be fine as there is no real current flowing through the control circuit of the pump.
    Or perhaps a multi tap transformer? Hmm... Work in progress. Except for the pipe. I finished that up to the indirect.

    So the circulator doesn't need to be big, haven't done the math yet but 6-10 gpm?
    Sorry for the long answer.
  • ZmanZman Member Posts: 6,002
    I don't know of a circulator that small that is both compatable with DHW and 0-10 VDC. Maybe something from the euro market? Grundfos?

    You could use a delta P circ and a 0-10 VDC modulating valve.

    A small and large circ piped in series would accomplish the same thing as well.

    A regular circ with a triac controller?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rodhot_rod Member Posts: 13,830
    If you run the first condition, that being overcoming the heat loss of the piping, you will have instant DHW at the remote tap. Really no reason to pump more gpm than that amount.

    I.E. leaves WH at 120, minimal heat loss arrives at distant fixture at maybe 115- 118°.

    What does make it more, most, efficient is turning off the pump when temperature is adequate in the loop :)
    A sensor at the remote faucet or at the pump return would be adequate to shut off pump when the loop is hot enough.

    The best money you could spend is getting all the hot water piping insulated to minimize that piping loss. I think some energy codes now require 1" wall insulation on hot water piping with recirculation.
    That could almost eliminate the need for recirc :) Or use some self regulating heat tape under the insulation, a few watts a foot would be adequate and may be less upfront and operating cost.

    I think you are spending dollars to save pennies with your plan?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • mikemac52mikemac52 Member Posts: 37
    @Zman Hmm, lots of fun things to think about. At first the 2 circs appealed but I would still need to fine tune the output of each.
    Could do Triacs if I went straight to a PLC would be easy, or if staying in the line voltage world, I could take a 3 speed circ. and wire that through relays. but again the fine tuning unless I got lucky. Delta P, constant pressure? That would probably be the prettiest way to go. Then I would just need to put the pump power on a relay.

    What is the most I could pump through a 3/4 inch line with say 12' of pipe head.

    I'm going to look for control valves tonight.

  • ZmanZman Member Posts: 6,002
    6 GPM is the most you really want to move water through a 3/4" pipe. If you were running this 24/7/365.25, I would recommend 1/2 that to minimize pipe erosion/corrosion. At 6 gpm the resistance would be 6.8' per 100'. You would usually add 50% to the actual length to account for fittings.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • ZmanZman Member Posts: 6,002
    I assume you know that the simplest and most inexpensive way to do this would be to insulate all the pipes and install one of many circulators on the market that turns off when the return temp hits the setpoint.

    Since I try to listen to the needs of the customer, I read this in your second post and am happy to enable. :)
    "First, I'm going to make this way more complicated than necessary...
    just cause I can."
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Dave H_2Dave H_2 Member Posts: 388
    I ran some numbers based upon what I was reading, if you have 1/2" copper, max gpm in the system in order to keep the velocity down should be 1.6 gpm. Here is a circ that can do that, it has a dial to set it for what you want.

    Here is also some of the math from here. Have a go at it yourself.

    Dave H.
    Dave H
    SuperTechAlan (California Radiant) Forbes
  • mikemac52mikemac52 Member Posts: 37
    edited October 15
    @hot_rod strange, your post didn't show till after I wrote my last reply. Guess I needed to refresh. Anyway Hi, nice to hear from you again.

    I did insulate the pipes 3/4 " with the nice flap but did not think about heat tape. I always thought of that tape as something to protect pipes from freezing. Do you really think I could do that and not recirculate?
    It would be a huge drag but I could split and re-glue and re-tape the insulation.

    I did place the sensor at the end of the line right where the recirc pipe begins. The controller has a delta T setting of 10 degrees which will cut out the pump at 110 and kick in when needed.
    The flow sensor was the other part of the equation to keep the pump mostly off and only work on demand.

    So the thing that got me started on this adventure is the spare temperature controller and an rtd I found myself with, courtesy of an under warranty repair of my indirect. So that part was no pennies, the plc I have laying around also but hydronics in new to me so would rather work out the mechanics/ timing of this first, program later. But since I haven't bought the pump or flow sensor yet...

    I'm just concerned of it not being enough. Even in the summer there is a decently long lag, winter is a different story. Water conservation is also a part of this. Water bill was a shock.

    What temp is the heat tape capable of maintaining?

    I see more research in my immediate future. I'm going to run some hot water and take temp readings over time to see what the insulation alone is doing. I'll come back with some more info.

    I haven't insulated the near boiler piping yet. Have some of the stuff, waiting for some elbows and tees.


  • mikemac52mikemac52 Member Posts: 37
    @Zman Lol, thanks.
  • BoilerToolboxBoilerToolbox Member Posts: 5
    You could use a Grundfos Comfort System. This includes a small UP pump with a built in timer that you install at the heater and a valve that gets installed at the fixture where you want instant hot water. The valve opens and closes based on temp and pressure differential, hence the need for the pump, but to be honest with you I installed a valve in my kitchen but never installed the pump and it works just fine. I have an old farmhouse with pipes that always froze because they ran through an uninsulated crawl space and putting this valve in has stopped the freezing for 5 years and running. 
  • hot_rodhot_rod Member Posts: 13,830
    Thermon Warm Trac
    these are all heat trace brands for DHW recirc, look around, it may or may not be an option for you.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • mikemac52mikemac52 Member Posts: 37
    Spent the day in the Doggie hospital. I'll get back to this soon. Thanks for the information.
  • mattmia2mattmia2 Member Posts: 1,861
    unless the tank is electric, the pump and aquastat is probably far more economical than the heat tape.
  • JUGHNEJUGHNE Member Posts: 7,183
    I have an indirect WH tank in the basement of a single story, it is about 60 horizontal pipe feet to my farthest plumbing fixture. 1/2" insulated return connected to the bottom of the tank at the drain valve. Ball valve for throttling before check valve (the only moving part) connected at the tank inlet. 7' vertical drop induces gravity flow.

    No pump or control.....just gravity.
    The continual very small flow of return water does loose some BTU's......(as would a pumped system) but how much before I reach the price of brass or SS pump and control ($300?), plus KW? .
    Then replace the pump someday.

    I have done recir systems in several commercial buildings with pumps, controls, high end mixing valves with at least 3 check valves.
    But as I age, simplicity for these things becomes more attractive,
    Alan (California Radiant) Forbes
  • JUGHNEJUGHNE Member Posts: 7,183
    This was clipped out in 1998.
    I applied it on my own house and a customer with a long run to the Kitchen, and if not working then a pump can be installed later.
    In both cases hot water is there right now.
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